1. Field of the Invention
The present invention relates to a flared end structure of a tube for forming a flared type pipe joint to be used in an automotive brake system or the like.
2. Description of the Related Art
A flared type pipe joint having a flared end structure of a tube is used widely for connecting tubes of a hydraulic circuit. Referring to FIG. 5 showing a prior art flared type pipe joint disclosed in JP-A 11-315976, a tube 10 is coupled to a nipple 11. The tube 10 has a flared end structure 12 formed by conically expanding one end part of the tube 10. The nipple 11 has an open end. A seat 13 is formed in the inner circumference of the open end of the nipple 11. The flared end structure 12 is pressed against the seat 13. A sleeve 14 is slidably put on the tube 10. The sleeve 14 has a pressing end pressed against the flared end structure 12. A coupling nut 15 is put on the sleeve 14. The nipple 11 has an externally threaded end provided with an external thread 16. The coupling nut 15 is screwed on the externally threaded end of the nipple 11 to press the pressing part of the sleeve 14 against the flared end structure 12 of the tube 10 to press the flared end structure 12 tight to the seat 13 of the nipple 12.
The flared end structure 12 of the tube 10 coupled to the nipple 11 by the prior art flared type pipe joint is expanded such that the expanded flared end structure 12 is capable of being elastically deformed so as to come into close contact with the seat 13. Specifications of flared end structures are specified in ISO standards.
The flared end structure 12 of the prior art flared type pipe joint is elastically deformed to make the flared end structure 12 come into close contact with the seat 13 by its resilience. Therefore, if the coupling nut 15 is screwed excessively on the externally threaded end of the nipple 11, the area of contact between the flared end structure 12 and the seat 13 increases and, consequently, contact pressured decreases and the sealing effect of the flared type pipe joint decreases. Thus, the sealing ability of the prior art flared type pipe joint is dependent on the degree of tightening the coupling nut 15 and the sealing effect of the prior art flared type pipe joint is insufficient for high-pressure piping.